他担心如果他放松警惕，有人可能会利用他。

He's worried that if he ___lets ___his ___guard ___down, someone may take advantage of him.

史蒂文斯即使在熟悉的情况下也从不放松警惕。

Stevens never ___lets ___his ___guard ___down, even in familiar situations.

在谈判中，直到协议签署前，你永远不应该放松警惕。

In negotiations, you should never ___let ___your ___guard ___down until the deal is signed.